HIGHER PROXIMAL DUODENAL MUCOSAL BICARBONATE SECRETION IS INDEPENDENTOF BRUNNERS GLANDS IN RATS AND RABBITS

Background & Aims: Duodenal bicarbonate secretion is impaired in patie nts with duodenal ulcer. Before characterization of any cellular trans port defect is possible, the origin of duodenal bicarbonate (epithelia l cells and/or Brunner's glands) must be determined. The aim of this s tudy was to determine the role of Brunner's glands in duodenal bicarbo nate secretion. Methods: Rats, which have Brunner's glands only in the proximal duodenum, and rabbits, which have Brunner's glands throughou t the duodenum, were anesthetized. Basal and stimulated (with HCl, pro staglandin E(2), and vasoactive intestinal polypeptide [VIP]) bicarbon ate secretion was measured in three isolated intestinal segments: prox imal duodenum, distal duodenum, and proximal jejunum. Mucosal surface area and Brunner's gland thickness was quantitated in each segment. Re sults: Secretion rates in proximal and distal duodenum and proximal je junum were significantly different. Normalized proximal-to-distal duod enal gradients in bicarbonate secretion were similar in the two specie s despite significantly different gradients of Brunner's gland thickne ss. In rabbits, gradients of bicarbonate secretion and Brunner's gland thickness were not correlated. In both species, HCl, prostaglandin E( 2), and VIP stimulated secretion in all three segments. If the agonist s specifically stimulated Brunner's gland bicarbonate secretion, relat ionships between gradients of bicarbonate secretion and Brunner's glan d thickness would have been anticipated. This was not observed. Conclu sions: The higher rates of bicarbonate secretion in the proximal duode num than in the distal duodenum and proximal jejunum are independent o f Brunner's glands.